The present invention relates to a fuel injection nozzle, especially for internal combustion engines.
A known fuel injection nozzle comprises a nozzle body and a valve needle having a closing head which is displaceably supported in a nozzle body and pressed opposite the fuel flow by a closing spring toward a first stop, which is fixed with respect to the housing. This valve needle is acted on in the opposite direction by fuel in the flow direction. The fuel injection nozzle also comprises a valve sleeve which is displaceably supported in the nozzle body upstream of the closing head of the valve needle and, together with the valve needle, defines a pressure space which is filled with fuel, and is provided in the area of this pressure space with lateral spray openings for directed fuel sprays and controls a valve gap for central fuel umbrella sprays with its front edge and a conical valve seat face at the closing head of the valve needle. The fuel injection nozzle also comprises a spring element for pressing the valve sleeve against the closing head of the valve needle into its closing position and also a second stop, which is fixed with respect to the housing, at which the valve sleeve, which first moves along the valve needle during the opening stroke, comes to rest after a pre-stroke which controls the lateral spray openings, so that the closing head is lifted from the valve sleeve and opens the valve gap for the central umbrella sprays of the fuel.
In a known injection nozzle of this type (DE-A1-32 13 751, FIG. 1) the first stop, which is fixed with respect to the housing and serves to support the valve needle in the closed position, is formed by an annular shoulder which is arranged upstream of the closing spring in the nozzle holder, the valve needle being supported at the annular shoulder via the valve sleeve and an additional tubular intermediate piece enclosing the valve needle. In this injection nozzle the closing spring simultaneously forms the spring element for pressing the valve sleeve against the closed head of the valve needle in its closing position. This construction has the disadvantage that the relatively thin-walled valve sleeve is subjected to a high impact stress due to the action of the strong closing spring when the valve needle impacts on the first stop, which is fixed with respect to the housing, and that, immediately after the valve needle lifts from this stop, the valve sleeve is only influenced by the pressures exerted by the fuel on both sides of the end faces of the valve sleeve. Accordingly, an unstable operating behavior results in which an exact timed sequence of the opening of the spray openings for the directed fuel sprays and of the valve gap for the fuel umbrella spray is not ensured. The same disadvantage is associated with another known structure (DE-A1-32 13 751, FIG. 5) in which the valve needle contacts a valve seat with its closed head in the closed position, the valve seat being fixed with respect to the housing; but again, and moreover also in the closing position of the valve needle, the valve sleeve is acted upon only by the fuel pressure, so that a defined opening sequence is not ensured.